Permanent magnet damping assembly for integrating meters



Feb. 5, 1963 PERMANENT Fig.l.

F. w. WITTE ETAL 3,076,934 MAGNET DAMPING ASSEMBLY FOR INTEGRATINGMETERS Original Filed June 16, 1954 mvNToRs Frederick W. Wi'r're 8 JohnJ. Loughron.

ATTORNEY sprains PERMANEIQT DAMPHNG ASSEMBLY FGR HQTEGRATHNG METERSFrederick W. Witte, Union, Ni, and .iohn .l. Loughran,

Pottstown, Pa, assignors to Westinghouse Electric Qorporation, EastPittsburgh, Pa, a corporation of Pennsylvania @rigfnai application .lune 16, 3354, Ser. No. 437,039. Divided and this application dune 26,E57, Ser. No. 667,634

4 Claims. (Si. 324-4152) This invention relates to permanent magnetassemblies and has particular relation to permanent magnet dampingassemblies suitable for damping rotation of rotor assemblics ofelectrical devices.

This application is a divisional application of application Serial No.437,030, filed June 16, 1954, by F. W. Witte and assigned to theWestinghouse Electric Corporation.

Permanent magnet assemblies are widely employed in the art for purposesof damping movement or rotation of the moving elements of variousdevices, such as relays, ammeters, voltmeters and wattmeters. Forpurposes of discussion, however, the present invention will be describedwith reference to permanent magnet assemblies employed in connectionwith integrating Watthour meters for purposes of damping rotation of therotor assemblies of such Watthour meters.

Such a permanent magnet assembly may comprise one or more permanentmagnets constructed of suitable high coercive magnetic material.Preferably, a pair of permanent magnets are provided with each magnethaving a substantially C-shaped configuration with a pair of opposedpoles defining an air gap. The magnets are conveniently mounted adjacentopposite edges of an electroconductive disc forming part of the rotorstructure of a watthour meter. With such positioning of the magnets,portions of the disc pass through the air gaps of the magnets during rotation of the disc.

The permanent magnets are conveniently secured in operative positions toa suitable frame member which is proportioned to support certain otheroperating components of the meter, such as the electromagnetic statorstructure and the rotor structure which include the electroconductivedisc. The frame may be constructed of any suitable material.Conveniently, the frame is a die-cast from an electroconductivenon-magnetic die-casting material with suitable spaced pockets of theframe being formed during the die-casting operation for receiving thepermanent magnets.

The present invention provides securing means for securing the magnetsto the frame within the pockets. In accordance with a specificembodiment of the invention, the securing means comprises a hardenablefluid material which is introduced into the pockets subsequent to themounting and positioning of the magnets within the pockets for rigidlysecuring the magnets to the frame.

With such arrangement the magnets are conveniently premagnetized priorto the insertion thereof into the pockets. Preferably, the securingmaterial is selected to have a melting temperature stuiiciently low toprevent alteration of the magnetic properties of the magnets duringassembly thereof.

Temperature compensating means in the form of C- shaped magnetic shuntsmay be associated With the magnets for the purpose of assuring asubstantially constant damping effect over a wide range of temperatures.Conveniently, the shunts are secured in operative positions relative tothe magnets within the pockets during the same operation by which themagnets are secured within the pockets.

The invention further provides locking means for preventing accidentalrelative displacement between the hardened securing material and thesupporting frame. The locking means comprises integral portions of theframe positioned and proportioned to engage the securing material tolock the material within the pockets.

It is, therefore, an object of the invention to provide an improvedpermanent magnet assembly.

It is another object of the invention to provide a permanent magnetassembly including a plurality of parts which are readily asembled anddisassembled relative to one another.

It is a further object of the invention to provide a permanent magnetassembly including a permanent magnet and a temperature compensatingmagnetic shunt secured within a preformed pocket of a supporting frameby a hardenable fluid material.

It is still another object of the invention to provide a permanentmagnet assembly including a G-shaped permanent magnet secured Within apreformed pocket of a supporting frame by a hardenable fluid materialhaving a re1- atively low melting temperature to thereby preventalteration of the magnetic properties of the magnet during assembly ofthe magnet relative to the frame.

It is a further object of the invention to provide an assembly asdefined in the preceding paragraph wherein the G-shaped magnet ispositioned within the pocket by movement of the magnet relative to theframe along an axis transverse to the plane of the magnet.

It is a still further object of the invention to provide a permanentmagnet assembly for an integrating watthour meter including a permanentmagnet secured within a pocket formed in a die-cast electroconductiveframe by a hardenable fluid material with the frame being proportionedto support an electromagnetic structure of the meter with theelectromagnetic structure extending across the open end of the pocket.

It is still another object of the invention to provide a permanentmagnet assembly including a permanent magnet secured to a supportingframe by a hardenable fluid material with means for preventing relativedisplacement between the hardened material and the frame member.

It is a further object of the invention to provide an improved method ofassembling a permanent magnet assembly relative to a supporting framemember.

Other objects of the invention will be apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a view in rear elevation with parts broken away of anintegrating watthour meter embodying the invention;

FIG. 2 is a view in section taken along the line II-II of FIG. 1;

FIG. 3 is a view in section taken along the line III-III of FIG. 1;

HS. 4 is a view in section taken along the line IV-IV of FIG. 1; and

FIG. 5 is a view similar to FIG. 4 showing a further embodiment of theinvention.

Referring to the drawings, there is illustrated in FIG. 1 an electricaldevice 1 embodying the invention. For purposes of discussion, it will beassumed that the device 1 comprises an integrating watthour meter,although the invention is applicable to other devices, such as relays,etc.

The meter 1 includes an electromagnetic stator structure including amagnetic structure 3 preferably constructed of a plurality ofmagnetically-soft stacked magnetic laminations 5, each having theconfiguration shown in FIG. 1. The laminations 5 may be secured togetherin any suitable manner to provide the magnetic structure 3. Thestructure 3 includes a single voltage magnetic pole 7 and a pair ofspaced current magnetic poles 9 and 11. The voitage pole '7 has a poleface which is spaced from the pole faces of the current poles 9 and 11to provide an air gap 13.

The voltage pole 7 is provided with a voltage winding 15 and the currentpoles 9 and 11 are provided respectively with current windings 17 and19. The windings 15, it! and 1% are effective when energized inaccordance with alternating quantities to establish a shifting magneticfield in the air gap 13 for influencing an associated rotor assembly.The rotor assembly includes a shaft 21 and an electroconductive disc 23mounted on the shaft 21 for rotation through the air gap 13. Furtherdetails of the construction of watthour meters of the type described maybe obtained by reference to US. Patent No. 2,512,- 345, issued to R. N.Leippe.

The present invention provides a supporting frame member for supportingcertain operating parts of the meter. With reference to FIG. 1, there isillustrated a frame 2.5 which may be constructed of any suitablematerial. Preferably, the frame 25 is constructed of a non-magnetic,elcctroconductive die-casting material, such as an aluminum die-castingalloy, which may be cast to provide a frame of the desiredconfiguration. Such diecasting material, being electroconductive, offersshielding against external alternating electromagnetic fields. Inasmuchas the frame may be cast separately, a material may be employed having asubstantial melting temperature, such as a temperature of the order of500 C. or higher. The material thus may be selected to provide desiredproperties such as physical, electrical and chemical properties withoutfear that the temperatures required will interfere with other operationsor components. The melting temperature of a suitable aluminum-basediecasting material is approximately 600 C.

The frame 25 is formed with a'pair of opposing sides 27 and 29 with theside 27 having projecting spaced surfaces 31 and 33 lying in a commonplane for a purpose appearing hereinafter. During the die-castingoperation, the frame 25 is conveniently provided with a pair of spacedbearing members 35 and 37 which are positioned on the side 29 of theframe and which are proportional to support the shaft 21 and the disc 23for rotation as will presently appear.

The frame 25 is further provided with one or more pockets 39 foraccommodating a permanent magnet assembly as will presently appear.Preferably, the frame 25 is formed with a pair of spaced pockets 3%arranged substantially symmetrically relative to the axis of rotation ofthe shaft 21. Each of the pockets extends from the side 27 of the framedownwardly as viewed in FIG. 2, and is provided with an end wall 43formed by a portion of the frame, and a side wall 47. As illustrated inPEG. 2, each of the end walls 43 is spaced downwardly from the open endof the pocket and is provided with an annular recess 51 whichcommunicates with the associated pocket.

Each of the end Walls 43 is provided with one or more openings 53positioned to communicate with the annular recess 51. In a preferredembodiment of the invention each of the end Walls is provided with apair of openings 53 proportional to form a pair of recesses 55 of eachof the pockets 39. As best shown in FIG. 3 each of the recesses 55defines a surface 57 of the associated pocket with the surfaces 57extending substantially transverse to the surfaces of the side walls 4-7of the pockets. The purposes of the surfaces '7 will be explained morefully hereinafter. Conveniently, the pockets, recesses and openings 39,51, and 53 all may be formed in the frame 25 during the die-castingoperation.

As best shown in FIG. 1, the frame 25 is provided with an elongated slot59 which extends entirely through the frame 25. The slot 59 isconveniently formed in the frame during the die-casting operation and isproportioned to communicate With each of the pockets 39 through the sidewalls 47 and through portions of the end walls 43 of the pockets. Itwill be recalled that spaced bearings 35 and 37 are provided on the side29 of the frame 25. The bearings 35 and 37 are proportioned to mount theshaft 21 and the disc 23 to position the disc 23 for rotation throughthe slot 59. The slot 59 is proportioned to provide small verticalclearance to permit passage of the disc 23 through the slot.

The frame 25 is proportioned with the magnetic structure 3 on the side27 of the frame to position the air gap 13 of the magnetic structure 3substantially in alignment with the slot 59 as illustrated in FIG. 1.With such arrangement, portions of the magnetic structure 3 engage theprojecting surfaces 31 and 33 of the side 27 of the frame with thewindings 15, 17 and 19 being received in a channel of the side 27 formedintermediate the surfaces 31 and 33. The magnetic structure 3 may besecured to the surfaces 31 and 33 of the frame in any desired manner. Asshown in FIGS. 1 and 2, the magnetic structure 3 extends across the openends of the pockets 39 to cooperate with the frame 25 for offeringshielding of the magnets 61 against external alternating electromagneticfields. The relative position of the magnetic structure 3, the slot 59and the disc 23 are best shown by reference to FIGS. 1 and 2. As shownin FIG.

1, the disc 23 is mounted for rotation through the slot 59 and the airgap 13 of the magnetic structure 3 under the influence of theelectromagnetic structure. The disc 23 is proportioned to have portionsthereof pass through the pockets 39 during rotation of the disc.

In order to damp rotation of the disc 23, a permanent magnet assembly isprovided which may comprise one or more permanent magnets positioned toinfluence the disc 23. Preferably, a pair of permanent magnets 61 isprovided with the magnets 61 being positioned at spaced points adjacentopposing edges of the disc 23 for influencing the disc. Each of themagnets 61 preferably is of substantially G-shaped configuration havinga pair of spaced poles defining an air gap 63.

The magnets 61 may be constructed of any suitable magnetic material.Preferably, the magnets 61 are constructed of a high coercive magneticmaterial a number of which are presently available. For example,highcobalt permanent magnet steel, such as one containing 36% by weightof cobalt is available. In a preferred embodiment of the invention, ahigh coercive alloy known as Alnico is employed. A number ofhigh-coercive permanent magnet materials are listed in a pamphletentitled Nickel Containing Alloys for Permanent Magnets published in1949 by the International Nickel Company, Inc, New York City. Such highcoercive alloys provide compact permanent magnets and have goodresistance to demagnetization. Alnico V and Alnico VI alloys are verysuitable. To illustrate suitable proportions, such as Alnico dampingmagnet may have an outer diameter of the order of 1% inches, a thicknessof the order of /2 inch and an air gap of the order of A; inch long.

Suitable temperature compensating means may be associated with one orboth of the magnets 61 for the purpose of providing a substantiallyconstant damping effect over a wide range of temperature. In thespecific embodiment of FIG. 1, a pair of magnetic members or shunts 65is provided each having a substantially C-shaped configuration definingan air gap 67. As will presently appear, each of the shunts 65 isassociated with a separate one of the magnets 61 with corresponding sidefaces of the associated magnet and shunt in engagement to position theair gaps 63 and 67 in alignment. With such arrangement, the shunts 65are effective to shunt magnetic flux away from the air gaps 63 of theassociated magnets 61. As is understood in the art, the shunts 65 may beconstructed of a material having a negative temperature coefficient ofpermeability. For example, the shunts may be constructed of anickel-iron alloy containing approximately 30% nickel.

In the past, a number of arrangements have been employed for mountingpermanent magnets relative to rotor structures. According to one knownarrangement, a pair of C-shaped magnets are die-cast with and embeddedin a die-casting support frame. With such arrangement it is necessary toperform the required machining operations on the frame with the magnetsembedded within the frame. Consequently, in order to avoid damage to thepermanent magnets such machining operations must be effected with greatcare. Furthermore, such arrangement of the magnets and the supportingframe may result in considerable waste of expensive parts inasmuch asfaulty machining of the frame requires disposal of both the frame andthe associated magnets by reason of the permanent nature of the mountingarrangement. During the die-casting operation of the above-describedprior art arrangement, relatively high temperature and pressureconditions are encountered which may result in damage to the permanentmagnets.

Acording to the above-described prior art arrangement, temperaturecompensating magnetic shunts are permanently secured to the magnetsprior to the die-casting operation, thereby requiring two distinctoperations involving the securement of the shunts to the magnets and thesubsequent die-casting of the assembled shunts and magnets with theframe.

In acordance with the teachings of the present invention, the magnets 61and the shunts 65 are secured to each other and to a performed framemember in a single operation to provide a rigid structure. The inventionfurther permits all machining operations to be performed upon the frameprior to the assembly of the magnets relative to the frame. The presentinvention further provides securing means for rigidly securing themagnets and the associated shunts in operative positions to the frame.

It will be recalled that pockets 39 are formed in the frame 25 duringthe die-casting operation. The pockets 39 are proportioned andpositioned to receive the magnets 61 and the associated shunts 65 tomount the magnets and shunts in operative positions relative to theframe 25. Although a pair of pockets 39 are provided for accommodating apair of magnets 61, a single pocket may be provided if it is desired toutilize a single permanent magnet to effect damping of the associatedrotor assembly.

According to the present invention securing means are provided forsecuring the magnets 61 and the shunts 65 to the frame 25 within thepockets 39. In a preferred embodiment of the invention the securingmeans is in the form of a hardenable fluid material which isconveniently introduced into each of the pockets 39 through one of theassociated openings 53 as by a die-castIng operation to engage themagnets 61, the shunts 65 and the frame 25. The invention furtherprovides that the fluid material be selected to have a meltingtemperature sufficiently low so as to prevent alteration of the magneticproperties of the magnets 61 during assembly of the magnets to theframe. The method of assembling the magnets 61 and the shunts 65relative to the frame 25 will now be described.

Prior to assembly of the magnets 61 and the shunts 65 relative to theframe 25, the frame 25 is machined and cleaned to provide a fini:hedframe member. Such operations assure that the slot 59 is clear of allforeign particles and that the frame member is properly proportioned toreceive the operating parts of the meter. If desired, the magnets 61 maybe treated and magnetized to a final magnetic condition prior toassembly thereof relative to the frame. After the above operations havebeen carried out, the magnets 61, the shunts 65 and the frame 25 arelocated in a suitable fixture assembly (not shown) in order to properlyposition the parts relative to each other.

-through the slot 59 and the air A separate one of the shunts 65 ispositioned within each of the pockets 39 with the side faces 69 of theshunts in engagement with the end walls 43 of the associated pockets.Each of the magnets 61 is located within a separate one of the pockets39 with the side faves 71 of the magnets in engagement with the sidefaces 73 of the associated shunts. The associated magnets and shunts arepositioned with the air gaps 63 and 67 thereof substantially inalignment.

The pockets 39 are proportioned to receive the associated magnets andshunts through the open ends there of by movement of the magnets andshunts relative to the frame in a direction transverse to the end walls43 While keeping the magnets and shunts parallel to their mountedposit'ons. The pockets are further proportioned to receive the magnetsand shunts in the m nner described with clearance to permit positioningof the magnets and shunts with annular gaps between the peripheralsurfaces thereof and the side walls 47 of the pockets, as best shown inFIGS. 1 and 2. The pockets are posi: tioned so that the aligned air gaps63 and 67 of the associated magnets and shunts are substantially inalignment with the slot 59 and the air gap 13 of the magnetic structure3 when the magnets and shunts are properly located Within the pockets.In addition, the pockets are positioned to receive the magnets with themagnets lying in a plane which includes, or which is adjacent to, theaxis of the shaft 21. I

With the magnets, shunt and frame positioned relative to each other inthe manner described, a hardenable fluid material '7 5 is introducedinto the space between the permanent magnets and the frame and allowedto solidify. Preferably, the fluid 75 is confined substantially to aC-shaped configuration terminating short of the ends of the permanentmagnets as shown in thedrawing. The cavity for receiving the fluid 75may be temporarily closed in any suitable manner as by pressingresilient material (not shown) into engagement with the magnets andframe. The hardenable fluid material, represented by the numeral 75, isthen introduced into the pockets or cavities through any suitableopenings such as the openings 53 to substantially fill the annular gapsbetween the peripheral surfaces of the magnets and shunts and the sidewalls of the associated pockets. The material 75 is positionedexternally of the slot 59 and the central openings of the magnets andshunts to permit passage of the disc 23 gaps 63. The material also fillsthe annular recesses 51 of the pockets and the openings 53 of the endwalls 43. Such material is conveniently introduced into the pockets 39as by a die-casting operation. The fluid material 75 is then allowed toharden with the result that the associated magnets and shunts ecomerigidly secured to each other'and to the frame within the pockets.

The material 75 may comprise any suitable hardenable fluid material,such as a plastic cement or adhesive, but preferably is a metallicalloy, such as babbit metal. which is capable of securing the magnets 61to the frame 25 upon setting. In accordance with a preferred embodimentof the invention, the material 75 is selected to have a meltingtemperature sufficiently low so as to prevent alteration of the magneticproperties of the magnets 61 during assembly thereof to the frame. Forexample, materials having melting temperatures of less than 250 C. maybe employed.

During the die-casting of the frame 25 the side walls 47 of the pockets39 are provided with a slope between the end Walls and the open endsthereof to provide enlarged open ends as shown in FIG. 3. It is alsoobserved with reference to FIG. 3 that the peripheral surfaces of themagnets 61 taper toward a side face thereof, and that the magnets 61 arepositioned within the pockets 39 to have the peripheral surfaces taperin directions toward the side 27 of the frame.

After the fluid material 75 sets, it is possible that the hardenedmaterial may subsequently become accidentally detached or loosened fromeither the frame 25 or the peripheral surfaces of the magnets 61 or fromboth. If for some reason the material becomes detached from theperipheral surfaces of the magnets, the magnets will still be firmlyretained within the pockets since relative displacement between thematerial and the magnets in directions extending toward the open ends ofthe pockets is prevented by engagement of the tapered surfaces of thematerial and the magnets. However, if the material eventually becomesdetached from the end walls and side walls of the pockets, the materialtogether with the magnets 61 are free for displacement relative to theframe 25 in directions extending toward the open ends of the pockets.

In order to prevent such accidental displacement of the magnets v61relative to the frame 25 means are provided in accordance with theinvention for securing the hardened material 75 against displacementrelative to the ,frame 25 in directions extending toward the open endsof the pockets. It will be recalled that each of the end walls 43 of thepockets 39 is provided with a pair of openings 53 proportioned to definesurfaces 57 of the associated side wall with the surfaces 57 extendingsub- .stantially transverse to the direction of extension of the pockets39. When the fluid material 75 is introduced into the pockets 39, thematerial substantially fills the openings 53 and the recesses 55 toengage the surfaces 57. By reason of the surfaces 57 accidentaldetachment of the material from the frame 25 is ineffective to free thehardened material for displacement relative to the ,frame in directionsextending toward the open ends of the pockets.

With reference to FIG. 5, there is illustrated a further embodiment ofthe invention wherein accidental relative displacement between the frameand the hardened material is prevented. In the embodiment of FIG. theframe 25 is provided with a pair of projections 77 each positioned toextend partially across a separate one of the open ends of the pockets.When the fluid material \75 is introduced into the pockets 3h, thematerial fills the annular gaps within the pockets to engage theprojections 77. Conveniently, the projections '77 are formed during thedie-casting of the frame 25 to extend along {axes parallel the axes ofextension of the pockets, as illus- '{trated in dotted lines in FIG. 5.Each of the projec tions may then be deformed to assume the position asshown in FIG. 5. For certain purposes, it may be desired to release .themagnets 61 from the frame 25 for permitting withdrawal of the magnetsfrom the associated pocxets. By means of the invention, the magnets areconveniently detached from the frame by the application of heat to thehardened securing material 75 sufficient to melt the material. Thepresent invention also permits the release of the magnets from the frameby forced detachment of the hardened material 75 from the frame. This isconveniently accomplished by striking the hardened material 75 with asuitable tool at the openings 53 of the end walls of the pockets toeffect disengagement of the hardened material from the frame and toforce the permanent magnet out of the pocket. The portion of thematerial 75 in the opening 53 constitutes in effect a rivet head and maybe broken off from the remainder of the material as the magnet is drivenout of the pocket.

Although the invention has been described as contemplating the provisionof a pair of permanent magnets 61 of identical configuration, and a pairof pockets 39 arranged symmetrically relative to the axis of the shaft21, it is to be understood that magnets 61 may be employed havingdifferent configurations, and that pockets 39 may be provided withconfigurations for accommodating magnets of different shapes.

By reason of the present invention, a rigid and compact damping assemblyis provided. The invention further assures against waste of expensiveparts in that the frame and magnets may be treated independently of eachother, and may be assembled relative to each other in a mannerpermitting ready disassembly thereof. Furthermore, the magnetsconveniently may be premagnetized prior to assembly thereof relative tothe frame. -In addition, the frame may be completely machined andcleaned prior to the mounting of the magnets to the frame. The magnetsare secured to the frame in an efficient and inexpensive manner whichassures against displacement of the magnets relative to the frame.

Although the invention has been described with ref- .erence to certainspecific embodiments thereof, numerous modificaitons are possible, andit is desired to cover all 'modifications falling within the spirit andscope of the invention.

' We claim as our invention:

1. In a watthour meter of the disc type, in combina- \tion, a thinwalled frame casting including a vertical wall having a horizontal slottherein to freely receive the disc, said wall having a relatively deeppocket cast therein at one end of said slot, a roughly C-shapedpermanent magnet assembly in said pocket and oriented to straddle theedge of the disc, said assembly including a relatively thick permanentmagnet and a superimposed thinner temperature compensator having anegative temperature coefficient of permeability, the pocket having afiat bottom wall engaging a portion of the bottom of said assembly, thepocket side walls flaring outwardly from the periphery of said bottomwall, the bottom wall having spaced holes therethrough, and a unitaryfilling of cast material in the space between the magnet assembly andpocket walls and extending through the said holes to secure the assemblyin said pocket,

2. In a watthour meter of the disc type, in combination, a thin walledframe casting including a vertical wall having a horizontal slot thereina freely receive the disc, said wall having a relatively deep pocketcast therein at one end of said slot, a roughly C-shaped permanentmagnet in said pocket and oriented to straddle the edge of the disc, thepocket having a flat bottom wall adjacent a portion of the bottom ofsaid magnet, the pocket side walls flaring outwardly from the peripheryof said bottom wall, the bottom wall having spaced holes therethrough,and a unitary filling of cast material in the space between the magnetand pocket walls and extending through the said holes to secure themagnet in said pocket.

3. In a watthour meter of the disc type, in combination, a thin walledframe casting including a vertical wall having a horizontal slot thereinto freely receive the disc, said wall having a relatively deep pocketcast therein at one end of said slot, a roughly 'C-shaped permanentmagnet assembly in said pocket and oriented to straddle the edge of thedisc, said assembly including a relatively thick permanent magnet and asuperimposed thinner temperature compensator having a negativetemperature coefiicient of permeability, the pocket having a fiat bottomwall and a side wall, said bottom wall having a hole extendingtherethrougn, said hole having an axis substantially passing through theintersection of said bottom wall and'side wall, and a unitary filling ofcast material in the space between the magnet assembly and pocket wallsand extending through the said hole to secure the assembly in saidpocket.

4-. In a magnetic damping assembly for damping rotation of an inductiondisc, a frame having a pocket with an open end, a bottom wall and a sidewall, a permanent magnet of substantially C-shaped configuration havingopposing C-shaped sides, said magnet having a peripheral surface betweensaid sides which tapers from one side toward the other side, said pocketbeing proportioned to receive said magnet through the open end, saidmagnet being positioned within said pocket with the peripheral surfacespaced from said side wall tapering toward said pocket open end, saidbottom wall having a $39 pair of spaced bales extending therethmugh,each of said heies having a center point on a line substantiallyparallel to and adjacent the packet side wall, and a. heatrneltablesoiid material in the space between the magnet and side Wall fillingsaid holes to secure the magnet in 5 said pocket.

Referenees Cited in the file of this patent UNITED STATES PATENTS600,751 Streeter Mar. 15, 1898 10 Reynolds June 17, 1902 Peters June 29,1926 Proctor Dec. 30, 1952 Goes Feb. 2, 1954 Riesz Mar. 24, 195) FOREEGNPATENTS Great Britain Sept. 8, 1935

1. IN A WATTHOUR METER OF THE DISC TYPE, IN COMBINATION, A THIN WALLEDFRAME CASTING INCLUDING A VERTICAL WALL HAVING A HORIZONTAL SLOT THEREINTO FREELY RECEIVE THE DISC, SAID WALL HAVING A RELATIVELY DEEP POCKETCAST THEREIN AT ONE END OF SAID SLOT, A ROUGHLY C-SHAPED PERMANENTMAGNET ASSEMBLY IN SAID POCKET AND ORIENTED TO STRADDLE THE EDGE OF THEDISC, SAID ASSEMBLY INCLUDING A RELATIVELY THICK PERMANENT MAGNET AND ASUPERIMPOSED THINNER TEMPERATURE COMPENSATOR HAVING A NEGATIVETEMPERATURE COEFFICIENT OF PERMEABILITY, THE POCKET HAVING A FLAT BOTTOMWALL ENGAGING A PORTION OF THE BOTTOM OF SAID ASSEMBLY, THE POCKET SIDEWALLS FLARING OUTWARDLY FROM THE PERIPHERY OF SAID BOTTOM WALL, THEBOTTOM WALL HAVING SPACED HOLES THERETHROUGH, AND A UNITARY FILLING OFCAST MATERIAL IN THE SPACE BETWEEN THE MAGNET ASSEMBLY AND POCKET WALLSAND EXTENDING THROUGH THE SAID HOLES TO SECURE THE ASSEMBLY IN SAIDPOCKET.